1. Field of the Invention
The present invention relates to a stencil-making-type printing machine in which plural types of rotary cylindrical drums having printing regions of different sizes can replaceably be loaded. In the printing apparatus, a stencil sheet or paper provided in the form of a roll is cut according to the printing region of a rotary cylindrical drum loaded therein to form a printing stencil, and a printing operation is carried out with the printing stencil wound on the rotary cylindrical drum. Before a printing operation is carried out for a new original, a used stencil is separated from the rotary cylindrical drum and discarded into a used-stencil accommodating box by a conveying means.
2. Background
Heretofore, in the case where a printing operation is carried out using a printing machine equipped with a rotary cylindrical drum having a printing region of a size corresponding to, for example, sheet size A3, a printing stencil, which is cut from a roll of stencil sheet and wound on the drum, always has to have a size which covers sheet size A3, even when an original to be duplicated or a printing sheet to be printed is smaller than sheet size A3. Hence, in the case where a printing machine of this type is used to obtain a small number of prints, the cost of the stencil sheet most significantly affects the printing cost per one print.
Considering the above points, a stencil printing machine has been proposed in the art according to which a plurality of rotary cylindrical drums having a printing region different in size among sheet sizes A3, B4 and A4 are prepared and the rotary cylindrical drums are replaced and loaded depending on the size of an original or printing sheet. These rotary cylindrical drums all have the same outer diameter, and in general the respective printing regions that permeate inks are common in their starting point which is located adjacent to the clamp provided along a generating line of the drum, but differ in their end point depending on the respective size. Therefore, the printing stencil in the form of a roll is cut and adjusted to a length according to the printing region of the selected rotary cylindrical drum, whereby the stencil sheet is saved and printing cost can be reduced.
When printing is started with a new original, the used-stencil is removed from the drum and is conveyed to a used-stencil accommodating box by a conveying means such as discharging rollers. In this case, unless the rotation amount of the discharging roller is greater than the rotation amount corresponding to the length of the used-stencil, the whole stencil cannot be accommodated in the used-stencil accommodating box. Therefore, the rotation amount of the discharging rollers is generally set somewhat greater than that corresponding to the maximum length (for example, size A3) of printing stencils usable in the stencil printing machine.
However, when a printing stencil shorter than the maximum length is wound on the rotary cylindrical drum, if the discharging rollers are rotated for discharging the stencil to the rotation amount as set above, the discharging rollers continue to rotate for a while even after the whole stencil is accommodated in the used-stencil accommodating box, and, there occur problems that the stencil once accommodated in the used-stencil accommodating box twines round the discharging rollers and is led out of the box again.